A new protosuchian crocodile from the Upper Triassic Elliot Formation of South Africa

A new protosuchian crocodilian, Baroqueosuchus haughtoni from the Upper Triassic or Lower Jurassic Elliot Formation of the Orange Free State is the most primitive protosuchian crocodilian known. There are no contacts between the quadrate and opisthotic or below the crania-quadrate canal, the internal carotid arteries were not enclosed in separate foramina and the basicranium was flat, with the basisphenoid being broadly exposed on the base of the skull. The basic diagnosis of the Order Crocodilia is discussed and a new diagnosis is offered based upon cranial anatomy.National Science Foundation, USA; Geology Foundation UT Austin, Texas, US

Comparison of beam theory and finite-element analysis with in vivo bone strain data from the alligator cranium

The mechanical behavior of the vertebrate skull is often modeled using free-body analysis of simple geometric structures and, more recently, finite-element (FE) analysis. In this study, we compare experimentally collected in vivo bone strain orientations and magnitudes from the cranium of the American alligator with those extrapolated from a beam model and extracted from an FE model. The strain magnitudes predicted from beam and FE skull models bear little similarity to relative and absolute strain magnitudes recorded during in vivo biting experiments. However, quantitative differences between principal strain orientations extracted from the FE skull model and recorded during the in vivo experiments were smaller, and both generally matched expectations from the beam model. The differences in strain magnitude between the data sets may be attributable to the level of resolution of the models, the material properties used in the FE model, and the loading conditions (i.e., external forces and constraints). This study indicates that FE models and modeling of skulls as simple engineering structures may give a preliminary idea of how these structures are loaded, but whenever possible, modeling results should be verified with either in vitro or preferably in vivo testing, especially if precise knowledge of strain magnitudes is desired. (c) 2005 Wiley-Liss, Inc

The Braincase and Neurosensory Anatomy of an Early Jurassic Marine Crocodylomorph: Implications for Crocodylian Sinus Evolution and Sensory Transitions

This is the pre-peer reviewed version of the following article: Brusatte, S. L., Muir, A. , Young, M. T., Walsh, S. , Steel, L. and Witmer, L. M. (2016), The Braincase and Neurosensory Anatomy of an Early Jurassic Marine Crocodylomorph: Implications for Crocodylian Sinus Evolution and Sensory Transitions. Anat. Rec., 299: 1511-1530., which has been published in final form at doi:10.1002/ar.23462. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving." You are advised to consult the published version if you wish to cite from it

The higher-level phylogeny of Archosauria (Tetrapoda:Diapsida)

Crown group Archosauria, which includes birds, dinosaurs, crocodylomorphs, and several extinct Mesozoic groups, is a primary division of the vertebrate tree of life. However, the higher-level phylogenetic relationships within Archosauria are poorly resolved and controversial, despite years of study. The phylogeny of crocodile-line archosaurs (Crurotarsi) is particularly contentious, and has been plagued by problematic taxon and character sampling. Recent discoveries and renewed focus on archosaur anatomy enable the compilation of a new dataset, which assimilates and standardizes character data pertinent to higher-level archosaur phylogeny, and is scored across the largest group of taxa yet analysed. This dataset includes 47 new characters (25% of total) and eight taxa that have yet to be included in an analysis, and total taxonomic sampling is more than twice that of any previous study. This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosauria and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades. Support values are low, suggesting rampant homoplasy and missing data within Archosauria, but the phylogeny is highly congruent with stratigraphy. Comparison with alternative analyses identifies numerous scoring differences, but indicates that character sampling is the main source of incongruence. The phylogeny implies major missing lineages in the Early Triassic and may support a Carnian-Norian extinction event.Marshall Scholarship for study in the United KingdomJurassic FoundationUniversity of BristolPaleontological Societ

Intraspecific variation in the skull morphology of the black caiman Melanosuchus niger (Alligatoridae, Caimaninae)

Melanosuchus niger is a caimanine alligatorid widely distributed in the northern region of South America. This species has been the focus of several ecological, genetic and morphological studies. However, morphological studies have generally been limited to examination of interspecific variation among extant species of South American crocodylians. Here, we present the first study of intraspecific variation in the skull of M. niger using a two-dimensional geometric morphometric approach. The crania of 52 sexed individuals varying in size were analysed to quantify shape variation and to assign observed shape changes to different types of intraspecific variation, that is, ontogenetic variation and sexual dimorphism. Most of the variation in this species is ontogenetic variation in snout length, skull depth, orbit size and the width of the postorbital region. These changes are correlated with bite force performance and probably dietary changes. However, a comparison with previous functional studies reveals that functional adaptations during ontogeny seem to be primarily restricted to the postrostral region, whereas rostral shape changes are more related to dietary shifts. Furthermore, the skulls of M. niger exhibit a sexual dimorphism, which is primarily size-related. The presence of non-size-related sexual dimorphism has to be tested in future examinations.Fil: Foth, Christian. Ludwig Maximilians University; AlemaniaFil: Bona, Paula. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentin

Integrated Diagenesis Study of Tight Gas Sandstone: The Permian Lower Shihezi Formation, Northern Ordos Basin, China

AbstractDiagenesis varies greatly from basin to basin and has been considered as the key control of the reservoir quality of tight sandstones. In this study, we analyzed the petrographic characteristics, diagenesis, and pore types and characteristics of the Permian Lower Shihezi Formation in the Ordos Basin. Results show that most of sandstones are litharenites with minor sublitharenites and feldspathic litharenites. The tight sandstones have ultralow permeabilities (averaging 0.67 mD) and porosities (averaging 8.35%), with pore-throat sizes ranging from 0.035 to 13.29 μm with 94.12% less than 5 μm. Overall, the tight sandstone reservoirs have undergone complex diagenetic alteration. Compaction and clay mineral cements are the two crucial diagenetic factors that controlled the tightness of the reservoirs. The compaction destroyed most of primary porosity, and the effective pores are mainly dissolved micropores, intragranular dissolved micropores, and micropores in clay minerals and mineral grains. The chlorite coating might have helped preserve a certain amount of porosity, but pore-lining chlorites significantly obstructed pore throats and reduced permeability. Results of the study provide insights and direct implications for the future success of exploration and production of the tight gas sandstone in the Ordos Basin and other similar tight sandstone reservoirs

Convergence and functional evolution of longirostry in crocodylomorphs

During the Mesozoic, Crocodylomorpha had a much higher taxonomic and morphological diversity than today. Members of one particularly successful clade, Thalattosuchia, are well‐known for being longirostrine: having long, slender snouts. It has generally been assumed that Thalattosuchia owed their success in part to the evolution of longirostry, leading to a feeding ecology similar to that of the living Indian gharial, Gavialis. Here, we compare form and function of the skulls of the thalattosuchian Pelagosaurus and Gavialis using digital reconstructions of the skull musculoskeletal anatomy and finite element models to show that they had different jaw muscle arrangements and biomechanical behaviour. Additionally, the relevance of feeding‐related mandibular traits linked to longirostry in the radiation of crocodylomorph clades was investigated by conducting an evolutionary rates analysis under the variable rates model. We find that, even though Pelagosaurus and Gavialis share similar patterns of stress distribution in their skulls, the former had lower mechanical resistance. This suggests that compared to Gavialis, Pelagosaurus was unable to process large, mechanically less tractable prey, instead operating as a specialized piscivore that fed on softer and smaller prey. Secondly, innovation of feeding strategies was achieved by rate acceleration of functional characters of the mandible, a key mechanism for the diversification of certain clades like thalattosuchians and eusuchians. Different rates of functional evolution suggest divergent diversification dynamics between teleosaurids and metriorhynchids in the Jurassic

Orbital cycle records in shallow unconsolidated sediments: implications for global carbon cycle and hydrate system evolution in deep-sea area sediments of the Qiongdongnan Basin

IntroductionMilankovitch theory has extensive application in sequence stratigraphy and the establishment of time scales. However, it is rarely applied to shallow strata rich in hydrates. Cyclostratigraphic analysis of the Quaternary unconsolidated sediments can help identify climate and sea level changes that correspond to orbital cycles and improve our understanding of the dynamic evolution of hydrates.MethodsUsing the natural gamma-ray log data from the deepwater area well W01 in the Qiongdongnan Basin, Milankovitch cycle analysis was conducted to identify the primary astronomical period in W01. Anchored to existing AMS-14 C age from bivalve shell as reference point, an astronomical age scale of W01 was established. Simultaneously, through the analyses of major trace elements and total organic carbon content (TOC) in sediment samples, how astronomical orbital cycles influenced past environmental conditions. Furthermore, employing sedimentary noise models, the relative sea level change of well W01 was reconstructed.ResultsSedimentary cycles of 27.34 m and 6.73 m were identified in the GR data from well W01, corresponding to orbital periods of 405 kyr and 100 kyr eccentricity, with a duration of approximately 2.5 Myr. The spectral analysis of paleoenvironmental proxies reveals a sedimentary cycle of approximately 27 m, while the sedimentary noise model reconstructs the fluctuating rise in sea level change. An obliquity modulation period of approximately 170 kyr was identified in the TOC data, which may reflect the combined effects of obliquity and other orbital parameters.DiscussionSpectral analysis of paleoenvironmental indicators showed that long eccentricity cycle had varying degrees of influence on changes in paleoclimate, paleosalinity, and paleoredox conditions. Additionally, a 1.2 Myr cycle was identified as a significant factor influencing sea level changes during the early Pleistocene in the South China Sea (SCS). In addition, it is confirmed that the dominant period of the glacial-interglacial cycle in the SCS from 0.6 Ma to the present is 100 kyr period. Synthesize the above analysis, during phases of low amplitude in the 405 kyr cycle or minimum value of the 100 kyr cycle, which are associated with lower temperature, conditions become more conducive to hydrate accumulation

The Effects of Biting and Pulling on the Forces Generated during Feeding in the Komodo Dragon (Varanus komodoensis)

In addition to biting, it has been speculated that the forces resulting from pulling on food items may also contribute to feeding success in carnivorous vertebrates. We present an in vivo analysis of both bite and pulling forces in Varanus komodoensis, the Komodo dragon, to determine how they contribute to feeding behavior. Observations of cranial modeling and behavior suggest that V. komodoensis feeds using bite force supplemented by pulling in the caudal/ventrocaudal direction. We tested these observations using force gauges/transducers to measure biting and pulling forces. Maximum bite force correlates with both body mass and total body length, likely due to increased muscle mass. Individuals showed consistent behaviors when biting, including the typical medial-caudal head rotation. Pull force correlates best with total body length, longer limbs and larger postcranial motions. None of these forces correlated well with head dimensions. When pulling, V. komodoensis use neck and limb movements that are associated with increased caudal and ventral oriented force. Measured bite force in Varanus komodoensis is similar to several previous estimations based on 3D models, but is low for its body mass relative to other vertebrates. Pull force, especially in the ventrocaudal direction, would allow individuals to hunt and deflesh with high success without the need of strong jaw adductors. In future studies, pull forces need to be considered for a complete understanding of vertebrate carnivore feeding dynamics

Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation

BackgroundCrocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known.Methodology/Principal FindingsWe measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research.Conclusions/SignificanceCritical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination